This patent deals generally with the cooling of capacitors, and more specifically with a capacitor which is cooled by a heat pipe.
It is well understood in the electronics field that the performance and life of capacitors is detrimentally affected by increased temperature. Capacitors normally have a maximum operating temperature, and since observing the maximum temperature is dependent upon removing heat from the capacitor, several devices have been used to cool capacitors.
These heat removal enhancements include removing heat from the external casing of the capacitor by increasing the thermal emissivity of the casing so that more heat will be radiated from the casing, moving air across the surface of the casing, and attaching fins to the casing to increase the surface area for heat transfer.
There have also been several efforts to remove heat from the center core of the typical cylindrical electrolytic capacitor casing. U.S. Pat. No. 4,264,943 to Anderson et al uses a hollow core for the capacitor to increase the surface area exposed to the cooler outside environment. In U.S. Pat. No. 5,673,168 by Efford et al, it is suggested that such a hollow core capacitor casing be cooled by natural or forced convection of a fluid through the hollow core. U.S. Pat. No. 3,622,846 to Reimers discloses building a capacitor on a spool formed from three heat pipes, one as the center core, and the other two as flanges in contact with the ends of the sheets wound around the core.
Each of these cooling arrangements suffers either from limited potential for cooling the capacitor or from high production costs. It would be very beneficial to have an effective means for cooling the core of a capacitor which does not require dramatic changes in the conventional capacitor structure.
The present invention provides heat pipe cooling for the core of a capacitor with only a simple modification in the structure of the typical capacitor casing.
The conventional capacitor is within an aluminum casing which is about 3 inches in diameter and 5xc2xd inches long. The casing is usually a drawn cup with the bottom and the cylindrical side made from one piece of aluminum, and the electrical terminals protrude from the top of the casing through an electrically insulating disc which seals what would otherwise be the open end of the cup.
The present invention requires only that an aluminum tube be inserted into the casing through the bottom, that the aluminum tube be located on the axis of the cylindrical casing, and that the end of the tube be sealed to the bottom of the casing. The aluminum tube is then used as a spindle for conventional construction of the capacitor by placing a conventional capacitor core around the aluminum tube with layers of foil separated by insulation wound around the core.
Cooling of the capacitor is accomplished by the use of a heat pipe placed within the axial tube and attached by the use of thermally conductive epoxy. The heat pipe casing either terminates at the bottom of the casing, leaving the bottom completely flat, or extends beyond the ends of the casing and is attached to auxiliary cooling devices. With either construction, because of the use of a heat pipe the entire core of the capacitor will be kept at essentially the same temperature as the end of the heat pipe which is being cooled by the casing or other devices.
If the heat pipe terminates at the casing bottom, the casing bottom can be cooled by placing it on a larger structure, such as a cabinet wall or electronic chassis, which conducts the heat away or dissipates the heat from its larger surface area. When the heat pipe extends beyond the casing ends, it can be attached to a fin assembly through which air is moved either by natural or forced convection. The ends of the heat pipe can also be cooled by circulating liquid around them.
The particular benefits of the invention are that it does not require modification of the internal structure of the capacitor or a heat pipe of special construction. The heat pipe used is a simple cylindrical heat pipe which can be manufactured in high quantity and inexpensively. The invention thereby furnishes reliably cooled capacitors at low cost.